Activated on 20 August 1942. The 340th Bombardment Group trained with B-25's for duty overseas. They arrived in the Mediterranean theater in March 1943. Assigned first to the Ninth Air Force and later (in August 1943) to the Twelfth. Served in combat from April 1943 to April 1945. Engaged chiefly in support and introductory missions, but sometimes bombed strategic objectives. Targets included airfields, railroads, bridges, road junctions, supply depots, gun emplacements, troop concentrations, marshaling yards and factories in Tunisia, Sicily, Italy, France, Austria, Bulgaria, Albania, Yugoslavia, and Greece. Also dropped propaganda leaflets behind enemy lines.

Participated in the reduction of Pantelleria and Lampedusa in June 1943, the bombing of German Evacuation beaches near Messina in July, the establishment of the Salerno beach head in September, the drive for Rome during Jan.- Jun. 1944, the invasion of southern France in Aug. and attacks on the Brenner Pass and other German lines of communication in Northern Italy from Sept. 1944 to Apr. 1945. Received a DUC for the period Apr. - Aug. 1943 when, although handicapped by difficult living conditions and unfavorable weather, the group supported British Eighth Army in Tunisia and Allied forces in Sicily.

Received a second DUC for the destruction of a cruiser in the heavily defended harbor of La Spezia on 23 Sept. 1944 before the ship could be used by the enemy to block the harbors entrance. Returned to the U.S., Jul. - Aug. 1945. Inactivated on 19 Aug. 1949.